1. Field of the Invention
This invention relates to a member used as a structural material for a semiconductor manufacturing apparatus such as a heat treating device or a diffusion treating device for a wafer, a CVD device or the like and a method for producing the same, and more particularly to a method for producing a member for a semiconductor manufacturing apparatus which is coated with a composite oxide film having excellent resistance to corrosion through a halogen compound or the like and resistance to metal release in a treatment under high vacuum.
2. Description of Related Art
Semiconductor elements are frequently manufactured by forming a film or the like for wiring or insulating layer onto a silicon wafer. As an apparatus for the manufacture of such semiconductors, there are an oxidation-diffusion device, a CVD device and so on. The oxidation-diffusion device is a device used for a treatment for the formation of an oxide film wherein steam (H2O) or oxygen (O2) made from a mixed gas of hydrogen (H2) and oxygen (O2) is introduced into a reaction vessel to form an oxide film onto a silicon wafer and for a treatment of diffusing an impurity such as phosphor (P), boron (B) or the like. And also, the CVD device is a device wherein several kinds of reactive gases are introduced into a treating furnace to form a desired film onto a silicon wafer through chemical reaction within a range of 300-1000xc2x0 C. In these devices, an inorganic material such as quartz or a metal material is used as a member constituting the reaction vessel for treating the silicon wafer, but the use of the metal tends to be eliminated. However, it is difficult that all the materials are non-metal inorganic material, which become disadvantageous in the cost.
It is usual that a metal material such as stainless steel (SUS316L) or the like is used in a portion exposed to an atmosphere in the reaction vessel among the members constituting the reaction vessel and a chromium passive film is formed on a surface thereof For example, as a technique of positively forming a chromium oxide onto a surface of a stainless steel substrate to improve a corrosion resistance, there is known a technique that the chromium (VI) oxide (CrO3) is chemically changed to form a hard film of fine chromium (III) oxide (Cr2O3) in JP-A-59-9171, JP-A-61-52374, JP-A-63-126682 and JP-A-63-317680.
However, the passive films of the chromium oxide disclosed in the above publications are not necessarily sufficient in the corrosion resistance to substrate. Because, it has been elucidated that a substrate material component (SUS316L) for these members adheres to the silicon wafer in accordance with conditions of a film forming process such as treating temperature and the like, which results in a metal contamination. Particularly, it has been confirmed that the contamination through the substrate metal material increases when flowing a reducing gas such as hydrogen and ammonia and when flowing a corrosive gas of a chloride, or when cleaning is conducted with a halogen compound such as chlorine trifluoride or the like.
Now, the stainless steel is known as a metal material having an excellent corrosion resistance and a surface thereof forms a passive film of chromium oxide (Cr2O3) by contacting with an atmosphere. Such a passive film is naturally thin in the thickness and is easily broken by erosion due to collision with particles or contact with an acid solution or the like, but is peculiar to have a property of reproducing the passive film through a self repairing action.
However, a chemical reaction for the reproduction is required to kinetically take a long time. Particularly, a part of a member constituting the semiconductor manufacturing apparatus is placed under a condition of alternately exposing to an atmosphere, a reduced atmosphere of a low oxygen and a reactive gas in a short time, so that there is caused a problem that an effect is not obtained to an expected level.
It is, therefore, an object of the invention to propose a technique for obtaining a member for a semiconductor manufacturing apparatus having excellent corrosion resistance and resistance to metal contamination.
It is another object of the invention to provide a member coated with a composite oxide film having excellent corrosion resistance to various corrosive gases and halogen compounds and resistance to metal contamination in a treatment under a high vacuum.
The inventors have made various studies for achieving the above objects and found that when a surface of a metal material substrate is coated with a chemically stable composite oxide film, a release of a metal atom from the substrate can be controlled and also an effective corrosion resistance can be obtained under a strong corrosive environment, and as a result, the invention has been accomplished.
That is, the invention lies in a member for a semiconductor manufacturing apparatus comprising a steel substrate and a composite oxide film formed on a surface thereof and comprised of silicon oxide-aluminum oxide-chromium oxide and a sintering aid.
In preferable embodiments of the invention, (1) the composite oxide film is made of a chemical densified film consisting of silicon oxide, aluminum oxide and sintering aid and amorphous chromium oxide fine particles filled in a space of the film and coating the surface of the film;
(2) the composite oxide film is formed by applying and firing a slurry containing silicon oxide, aluminum oxide and sintering aid to form a chemical densified film, and applying an aqueous solution of chromic acid and sintering aid thereonto and firing at a temperature of 250-750xc2x0 C. to precipitate amorphous inorganic composite fine particles consisting of chromium oxide and sintering aid in a space of the substrate and onto the surface of the substrate;
(3) the sintering aid is a material of at least one selected from borate compounds, silicate compounds and phosphate compounds producing amorphous inorganic substance through sintering.
Furthermore, the invention lies in a method of producing a member for a semiconductor manufacturing apparatus which comprises applying and firing a slurry containing silicon oxide, aluminum oxide and a sintering aid onto a surface of a stainless substrate to form a chemical densified film, and then applying or spraying an aqueous solution of chromic acid containing a sintering aid onto a surface of the chemical densified film or immersing in this aqueous solution and firing at 250-750xc2x0 C. to form a composite oxide film consisting of silicon oxide-aluminum oxide-chromium oxide and sintering aid.